Tunnel kiln



.T. LARSSON June 10, 1930.

TUNNEL KILN F1166 March 26,. 1926 2 sheetssheet 2 W d w 4 L.. 5....?. ....TrFnZ-.nea f ////r l l All In' .f Il AI l /ll Il lll/ /f f//ff//f Patented Juney 10, 1930 i iJNITED STATESPATENT oF'Flcr.N i

' THURE LARSSCN, OF WORCESTER, MASSACHUSETTS, ASSIGNOR TO NORTON COMPANY,

OF WORCESTEIL MSSACHUSETTS, A CORPORATIOMYOF MASSACHUSETTS TNNEL KILN Application led March 26, 1923. Seria1-N'of26467.

The present' invention relates to tunnel lkilns, andl more particularly to tunnel kilns of the muflle type. ,In this type of kiln the wareto be heattreated travels on cars between gas 'or oil heated# muflles. The products of combustion generated in the firing Zone ordinarily pass through pipe extensions of the inutiles into a preheating Zone, interposed between the firing zone and the entrance to the kiln, and therefore subjects the ware to an initial heat considerably less than the treating heat in the tiring zone. This type of kiln is-also provided with a cooling zone interposed be-A 1 5 tween the exit to the kiln and the firing Zone from which the cooling zone is separatedso that the only'heat inthe cooling zone is produced by radiation from the heat-treated ware traveling therethrough. Various types'of Inutile have been heretofore used to protect the ware from contact with .the products of combustion, and nu merous ,difficulties have been met in the attempt to providean inexpensive and yet efficient muflie construction which will withstand the very high temperatureto which the muile must be subjected. One common form of mulie is a b oxlike structure having double walls" and intermediate partitions'. This is ejpensive to make and there -is consider-able danger of breakage, during manufacture,

handling andluse owing to the fragile nature of the ceramic materials of which it is made.

It is extremely important that the kiln operate continuously. and without interruption,

" since any enforce-d shutting down of its operation may result in the loss of a large amount of partially fired ware. Hence, it is highly desirable that vthe muiiie be-capable not only of transmitting heat readily to the ware, but

it should above all be so constructed and arranged that it will not fail under normal tiring conditions.

' There is considerable waste of heat in the operation of a tunnel kiln, which should be The principal object of the present'invention isto provide a tunnel kiln of the Inutile type which will be simple in its construction, inexpensive to buil'dand efficient in its operation, and particularly to provide a muie Aconstruction 'which is made up of plates and other simple parts capable of being easily assembled at the pointl of use.-

' Another object of the present invention is to provide a tunnel kiln with improved means for withdrawing the hot gases therefrom which are utilizedto preheat the air-used in the burners which heat the kiln.

To the accomplishment of these objects, and such others as may hereinafter appear, the various features of the present invention consist in certain devices, combinations and arf rangements of parts fully set forth hereinafter,the advantages of which will be readily. understood by' those skilled in the art.

The various features of the present invention will be explained in connection with the Jaccompanying drawings illustrating one embodiment of theinventiomin which,

Fig. l is a front sectional elevation of a tunnel kiln;

Fig. 2 is a fragmentary 'detail in perspective of the laterally corrugated partition which form the front wall of the muiiie;

Fig. 3 is a fragmentary detail of the cap, in underside plan, the muffle partition being shown insection and partly broken away;

t nd. Y, Fig. 4.- Vis a somewhat diagrammatic sec-' tional plan, taken partly Yon the line lf-4 of Fig. l, with certain parts of the heat eX,

away to'illustrate the operation of the kiln'.

The various features of the present inven tion are embodied in av tunnel kiln of the mutlle type in which the combustion gases do not contact with the ware. In 'the specificv form illustrated, a tunnel kiln is provided having foundation walls 1 -upon which are built the outer vertical 'side walls 2 which are joined together vby the roof 3' and heldin place, by means of suitable steel girders and cross rods. The foundation walls l andthe sidewalls 2, which are composed-principally of refractory bricks, are-supported on a pris'.

Achange systemL also shown partly broken j y 5 facilitate the passage of a car 7, loaded with the'ware tobe treated, through the kilnfrom the entrance 8, Fig. 4, to the exit 9. The Ware may be supported Within saggers upon a body of refractory blocks carried by a4 refractory base 11, supported by the car 7. On each side of the passage Within which the car travels are the benches -12 and 13 built up of the brick Work' of the kiln. These benches form the bottoms of the mufes, as 15 will be'later described. To prevent undue v-transmission of heat from the heating chamber to the outside of the kilnA and to better insulate the kiln, a layer of suitable material of low heat conductivity, such as diatomaceous earth, Silo-Cel or the like, is placed over. the top of the roof wall and a similar filling is-placed in the spaces Within the side Walls throughout the length of the kiln.

In the illustrated embodiment of the invention, the vkiln `is provided 'with three zones, namely, a firing zone 14, a preheating zonev`l5, (Fig. f4), and 'a cooling zone 16. Upon one side of theroadway the firing zone 14 is provided with a series of burners located in the spaces 17 in the furnace wall, each burner 18 being suitably supplied with liquid fuel or gas and air rom'headers 19 and 20, respectively. -The opposite side of the kiln is also provided with another series of four combustion spaces 21, each of which is provided with a burner 22, to which liquid fuel or gas and air are supplied from headers 23 and 24, respectively. n

The flame from the burners is enclosed in a muilie formed by the bench floors 12 and 13, the kiln Walls 25 land 26 and a series of muliie plates 27 and-28 adjacent to the Ware. The muliie plates are referably made of ceramic bonded super-re ractory granules, such as crystalline alumina or silicon carbide, and the kiln Walls forming the sides and bottoms of the muilies may be made of similar material.

The tops of the Walls 25 and 26 support skevvbacks 29 and 30 for the arch 31, Which extends over the Ware-road 5 and forms the top of thekiln. In order to support the bottoms of the muille plates, the benches 12 and `13 are each provided with alongitudinal channel 32 in Whichvsectionsof therefractory mullle plates are inserted by engaging the bottom edge face of the partition loosely in the 'channel Each muille plate is preferably corrugated laterally, as shown in Fig. 2, in order to strengthen it and to increase the area of its exposed surface whereby heat is transferred from the, combustion chamber to the ware in the road. As shown particu- 05 larly in Fig. 1 the muille plates in the channels 32 overlap one another throughout the length of the Ware-road thus serving to partition the Ware-road from the adjacent Walls of the kiln throughout the three zones thereof. In order to maintainthe muiiie plates in the channels 32, the Walls 25 and 26, and their continuations throughout the length of the kiln, are each provided with a series of projecting blocks 35 having upstanding lugs 75 36 thereon. Bridging the space between the blocks 35 and the top of each muille plate, is a movable cap 37 constructed to have a loose intertting engagement with the lug 36 and ,a loose engagement with the top of the muiile so plate. In this manner, Athecap 37 is removably connected to Walls 25 and 26 respectively, thus serving as a top to the muilie and a support for the muiile plate. As shown in Fig. 3, the bottom of the ca 37 85 is provided with a staggered series o depending lugs 38, arranged to loosely embrace the opposite side faces of the Inutile plate. This cap 37 also has a channel 34 Which interits with the upstanding lugs `on the blocks 35, thereby holding the cap securely 1n position.

With this construction the muiiie plates are easily put into place and they effectively protect the Ware from the products of combustion while allowing suilicient heat to be transmitted therethrough to treat the ware. In the event of an accident in the kiln any displaced Ware will merely knock the loose'y partition and the loose cap down Without 10 y injury resulting to the permanent structurev of the benches, combustion or cooling vchamber Walls, or the arch and Without dangerv of obstructing the passage of the Ware train through and out of the tunnel. The partitions and caps are comparatively inexpensive and can be readily removed and replaced.

. It will be observed that the mulles are lmade in two-sections separated by partitions 70 yso that the air in the muilies in the cooling zone does not mix with the burning gases in the heating zone. .The air entering Withi the burning oil forms highly heated products of combustion, and if these are too hot to 'be' passed safely through the valved passages 50,5115 the heat exchange apparatus, cooling air may i be introduced intothe muflie through passages 39 in the furnace Walls. These heated A gases in the preheating Zone 15 are withdrawn through vertical flues 40 and 41 con- 1.20

necting the combustion chamber with a horizontal flue 42 which discharges into the first section of a heat exchange device 43 in which the air for the burners preheated. p In order to cool the zone 16, which is heated only by the heat radiating from the ware through the m'uihe plates 27 and 28, the Walls in the zone lfcorresponding to the Walls 25 and 26 inthe yfiring zoneare provided with a series of spaced vents 44. to permit fresh air to enter the mulilei This air is heated by the ware and then withdrawn from the cooling zone through dampered passages into the vertical flues 45 and 46 which connect thel cooling zone with a horizontal flue 47 connected to theA second section-'of the heat exchange device 43.

In order to withdraw the products of combustion and the -heated air from the preheating zone and the heated air from the cooling zone, discharge them into the heat exchange device 43, and then withdraw them from the preheater and discharge them into the atmosphere, two4 blowers 48 and 49 are provided. Only one blower is used at a time,

' but in the event one of the blowers is put out ofcommission the emergency blower can be instantly cut into the induction system.

Both blowers areconnected to a horizontal pipe or vflue -50 which communicates, with a short horizontal pipe 5l connectedv by short flues 52 and 53 to the first and second sections of the heat exchange device. The blower 48 a branch 56. As shown'in Fig. 4 the flue 50 is provided with dampers 57 and 58A. Vhen the blower 48.A is shut down thedamper 57 is closed and -the damper 58 is opened to permit the blower 49 to withdraw' the products of combustion and the heated air from by dampers 59 and 60.

In order to preheat the air for the burners in the heat exchange device' 43, two fans 6l and 62, one forV emergency, are provided.

'I These fans discharge fresh air into a main 63 which for a portion of its length 'passes through both sections of the heat exchange device. The main 63 vis connected by branches 64 and 65 to the hot air headers 20 and 24, respectively. With this arrangement the air for the burners is highly heated without intermixture with the products of com- -bustion In order to control the temperature of the heat exchange device the first section thereof and the horizontal ilues 42 and 47 havel open ends Vprovided with dampers 66, l67 and 68 respectively. When these dempers 4are closed the' temperature is high but this temperature can be reduced by controlling'the admission .of-fresh air into the system through these dampers. AThe vertical flues 40,'41, 45 and 46 likewise are each provided witha damper 69 The blower-49 dis-v A the Ioutsi'depipe of the heat exchange device.

Gold air may be admitted to these hot gases 4both in the inutiles, by means of regulatable' openings 39, and in the flue 42 by means of damper 67. The `temperature of the heat exchange device may be regulated by damper Likewise, air is admitted to the cooling mufle in zone 16V through the succession of regulatable openings 44, of which there are a-series along the sides of the kiln, and this air is drawn through the mufflcs, absorbing heat throughthe inner mulile wall plates, and thenlinto'the pipes 45, 46 and the cross pipe 47 into the second sectionof the heat exchange device. The temperature of the air entering the heat exchange device maybe,

control-led by means of the damper-ed open- .ingv in the pipe 47.' The air which goes to the burners passes through the inner pipe 63 and absorbs lieat from the surrounding gases,

and the temperature thereof may be'. regulated as desired. i The muffles', as explained, are formed primarily of the sections of overlapping Inutile plates 27, 28 supported freely from the kiln'- side walls and muffle benches. The `plates are held in place by tbe-grooves 32 in the benches and by the caps which rest 4freely thereon. The joints may be packed with suitable refractory material, if desired, but it is never: theless a fact that the ninflle' plates are free to move as they expand or contract. The plates are preferably strengthened by corrugations arranged vertically. The plates may be made in the simple form shown by ordinary ceramic operations and .with the minimum danger of loss by breakage. Their composition may be determined by' kiln re q'uirements, as is well understood, but one satisfactory plate may be made of selected sizes of crystalline alumina grains bonded by highly refractory Vclays and other ceramic materials vitrified at a temperature. above that to which they will be exposed duringuse.

It will be apparent to those skilled in the art that various changes maybe made in the details of construction, The described and illustrated embodiment ofthe invention being intended as an exploitation of its underlying essentials, the features whereof will be definitely stated in vtheir true scope in thc claims heretoappended.

4products of combustion leading from said device, and means for mixing a cooler gas 'with the products of combustion before they enter the exit iiue.

2. A tunnel kiln comprising a firing zone and a cooling Zone, a inutile in the cooling Zone, a muflle and a burner therein in the firing zone, an air conduit to supply'air to the burner. means for delivering fresh air into the muiile in the cooling zone, a heat exchange device to heat the air supplied to the burner muiiic, and means for withdrawing the air heated in the cooling muil'le and delivering it to the heat exchange device.

A tunnel kiln having a tiring and a cooling z one, a inutile and a burner associated thcrewitlrin the firing Zone, means for delivering air to the cooling zone, a preheating device having inlet and outlet conduits connected to discharge the products of combustion from the burner inutile and a conduit to supply preheated air to the burner, a blower in said outlet conduit, and means for mixing the air heated in said cooling zone with the products -of combustion before they pass through the blower.

l. A tunnel kiln comprising a firing zone and a preheating Zone connected so that the products of combustion generated in the fir- 'ing zone pass through the preheating Zone,

a cooling Zone, a muiiie and a burner in the iii-ing Zone, an air conduitto supply air to the-burner, means for delivering fresh air into the cooling Zone, a sectional heat exchange device to preheat the air supplied to the burner, and means for withdrawing the products of combustion from the tiring and the preheating zones and `delivering them to one section of the heat exchange device and for withdrawing the air heated in the cooling Zone and delivering it to the other section thereof.

5. In a kiln, a firing zone, a heat exchange' device arranged to preheat` air supplied to the kiln, means for withdrawing the products of combustion generated in the tiring zone and delivering them to the heat exchange device, and means for controlling the temperature of the air heated by said device.

G. A tunnel kiln Comprising a firing zone and a preheating Zone connected so that the products of combustion generated in the firingr Zone pass through the preheating zone, a fuelv burner and an air supply duct leading thereto in the firing zone, a cooling zone,

means for delivering fresh air into the cooling zone, a sectional heat exchange device, means for withdrawing the products of combastion and Vtheair heated in the preheating zone and delivering them to one section of said device, meansfor withdrawing the air heated in the 'cooling zone and delivering it to the other section of the heat exchange device, and means for differentially controlling the temperature in the sections of the heat exchange device. l

7. A tunnel kiln comprising a firing zone and a preheating Zone connected so that the products of combustion generated in the firing Zone pass through the preheating zone, a heat exchange device, and means communicating with the preheating zone for withdrawing the productso'f combustion there from and delivering them to said device, in-4 cl`uding a flue and controllable means for admitting fresh air to the flue.

8. A tunnel kiln comprising a firing Zone and a preheating zone connected so that the products of combustion generated in the firing zone pass through'the preheatingzone, a heat exchange device, means communicating with the preheating zone for withdrawing the products of combustion therefrom and delivering them to said device, and controllable means for admitting fresh airto the heat exchange device to modify the temperature thereof.

9. A tunnel kiln comprising a firing zone provided with a series of burners on opposite sides and at different locations longitudinally thereof, means for delivering fuel to the burners, branch air pipesA for delivl ering air to the two series of burners, a main connected to the branches, a heat exchange device for heatingthe air in the main, means for withdrawing the products of combustion generated in the firing zone from the kiln and delivering them to said device, and means to mix cool air with said'products of combustion before they are passed to the exterior atmosphere.

l0. A tunnel kiln having a tiring Zone, a

inutile and a burner associated therewith in said tiring zone, a preheating device having inlet and outlet conduits connected to discharge the products of combustion from the mulie and a conduit for delivering preheated air to the burner, a blower in said outlet conduit, and means for supplying a cooler gas to cool the products of combustion before they enter the blower. Y

11. A tunnel kiln having a firing Zone, a4

muflle and a burner associated therewith in said tiring zone, conduits for conducting fuel and air to-the burner, an outlet conduit connected to discharge the products of combustion from the muflc, a blower in said outlet .eondnit,'and regulatable means for supply ing a cooler gas to cool off the products of combustion before they enter the blower.

' 1.2. Atunnel kiln comprising a bench, a

kiln wall rising therefrom, and a cap pre- ]ecting laterally from the wall adjacent its top, and a'mutile plate interposed loosely between the bench and the cap.

13. A tunnel kiln comprising a bench, a

kiln Wall rising therefrom, a cap loosely supported from the Wall near its top and 'projecting laterally therefrom, and a corrugated Inutile plate of super-refractory material interposed loosely between the bench and the cap.

14. A tunnel kiln comprising a channeled bench, a kiln Wall-rising therefrom, and a cap projecting laterally from the wall ad- ]acent to its top, s aid cap having on its lower face a plurality f staggeredlugs, and a laterally corrugated refractory muliie plate having its bottom edge engaged in the bench channel and having its top' edge engaged with the cap between the lugs which embrace the opposite side faces of the muflie plate.

l5. A tunnel kiln comprising a bench, a kiln Wall rising therefrom and having a pro- -the side Wall, which forms thev top of the muftle and serves to support the muliie plate. 17. A tunnel kiln comprising side, top and bottoni Walls delininga chamber through which lWare may be transported, a bench forming the bottomv of the inutile, a series of corrugated refractory plates supported on the bench and members loosely supported from the kiln side walls which engage and hold the topsl of the plates in position and form the top of the Inutile.

1R. A tunnel kiln Inutile comprising a bottom and two side Walls arranged to form an extensive combustion chamber, said bottom and a side vWall havin'ga `nfroove and a port-ion intertting therewith. and a 4removable cap havinf;r a portion interfitting with thel top of one side Wall to connect it with the other.

Signed at lVorcester. Massachusetts, this 22nd day of March, 1928.

`THURE LARSSON. 

